Suzanne Devine Clark places stones at a memorial outside the school during the one year anniversary of the shooting death of 17 at Majory Stoneman Douglas High School Thursday, Feb. 14, 2019 in Parkland, Fla.
The Miami Herald/Al Diaz via Getty Images

On February 14, 2018, a gunman opened fire at the Marjory Stoneman Douglas High School in Parkland, Florida.

The deadly school shooting left 17 students, faculty, and staff members killed, and another 17 injured.

This timeline, constructed from The Broward Sheriff's Office official records and surveillance footage, outlines how the massacre unfolded.

One of the deadliest mass shootings in the United States took place one year ago at the Marjory Stoneman Douglas High School in Parkland, Florida.

Fewer than two hours after the gunfire first broke out, authorities arrested a single suspect: 19-year-old Nikolas Cruz, who had formerly been a student at the school.

The massacre left 17 students and staff members killed, and reignited a nationwide debate over gun control. Cruz remains behind bars, and could face the death penalty if prosecutors pursue a trial.

One year after the shooting, students, staff, and families have gathered at the school to remember the victims.

Here, moment by moment, is how the event unfolded.

Brennan Weiss contributed to an earlier version of this report.

2:19 p.m.: The suspect in the shooting, then-19-year-old Nikolas Cruz, arrived at Marjory Stoneman Douglas High School via an Uber.

Law enforcement officers stand outside Marjory Stoneman Douglas High School on the one year anniversary of the mass shooting on February 14, 2019 in Parkland, Florida.
Getty Images/Joe Raedle

2:22 p.m.: The school's fire alarm goes off, prompting students to begin evacuating. This is also when the first 911 call went out.

2:23 p.m.: The school resource officer, Deputy Scot Peterson, issues a radio alert warning of shots fired. "Be advised we have possible — could be firecrackers. I think we have shots fired, possible shots fired, 1200 building," he said.

Marjory Stoneman Douglas High School is pictured in an aerial view in Parkland, Florida, U.S. February 15, 2018.
Reuters/Thom Baur

2:28 p.m.: Cruz exits the school and runs toward the tennis courts and heads south. He blends into a crowd of students as they flee the campus.

2:32 p.m.: Four Coral Springs police officers and two Broward County sheriff's deputies entered the building for the first time. The sheriff's department would later face intense scrutiny over the length of time they waited before entering.

February 15, 2018: Cruz appears in court for the first time via video. He is charged with 17 counts of murder, and his public defender describes him as a “deeply troubled child who has endured a lot of emotional trauma in a short period of time.”

March 14, 2018: A judge enters a "not guilty" plea on Cruz's behalf. His attorneys have repeatedly offered to enter a guilty plea if prosecutors will vow not to pursue the death penalty. Prosecutors have rejected that deal, meaning a lengthy death-penalty trial is likely.

Nikolas Cruz is lead into the courtroom before being arraigned at the Broward County Courthouse in Fort Lauderdale, Fla., on Wednesday, March 14, 2018.
South Florida Sun-Sentinel/Amy Beth Bennett via Associated Press

February 14, 2019: The one-year anniversary of the shooting occurs. Students, families, and staff members spend the day remembering the 14 students and 3 staff members who died.

Peter Palmer of the Margate Fire and Rescue CERT chapter wipes away tears at the memorial garden outside of Marjory Stoneman Douglas High School Thursday, Feb. 14, 2019 in Parkland, Fla., on the one year anniversary of the shooting at the school.
South Florida Sun-Sentinel/Joe Cavaretta via Getty Images